[0001] This invention relates to a coupling as specified in the preamble of claim 1, for
example as disclosed in US-A-1,900,208.
[0002] The invention is particularly concerned with a coupling for driving the shaft of
an ignition distributor from the camshaft of an internal combustion engine, where
in practice the camshaft and distributor shaft are located in a coaxial relationship
with the ends of the shafts facing each other.
[0003] The problem underlying the invention is that'of providing an improved coupling of
the type described that can accommodate misalignment between the camshaft and distributor
shaft, that is effective to reduce noise associated with drives of this type, and
that is capable of damping engine torque pulsations which might otherwise be applied
to the distributor shaft.
[0004] For solving this problem, a coupling in accordance with the present invention is
characterised by the measures specified in the characterising portion of claim 1.
[0005] In a preferred form of coupling in accordance with the present invention, a driving
member formed of plastics material has integral drive lugs extending from one face
thereof that are engaged in a groove formed in the end of the camshaft. The opposite
face of the plastics driving member has projecting drive lugs that are engaged within
aligned grooves formed in a metallic driven member that is connected to the distributor
shaft. An elastomeric sleeve is disposed about each of the drive lugs that are located
in the grooves of the metal driven member, whereby the transmission of torque between
the members takes place through the elastomeric sleeves. The plastics driving member
has flexible (resilient) arms that extend through slots formed in the metal driven
member and have teeth engaging the metal driven member for securing the plastics member
to the metal member. However, the arms can slide in slots formed in the metal driven
member, to permit relative radial movement of the two coupling members. This radial
movement is along an axis which is substantially perpendicular to the axis of the
drive lugs that engage the groove in the end of the camshaft.
[0006] A coupling as described permits relative movement between the coupling members along
an axis substantially perpendicular to the axis of the groove in the end of the camshaft.
The elastomeric sleeves serve to damp vibration, to reduce noise associated with drives
of this type, and to damp or smooth out engine torque pulsations that might otherwise
be transmitted to the distributor shaft, in any relative position of the coupling
members, since the elastomeric sleeves slide with the plastics member relative to
'the metal driven member.
[0007] In the drawings (the various Figures of which are not all to the same scale):
Figure 1 illustrates an ignition distributor connected to'the camshaft of an internal
combustion engine by a coupling in accordance with the present invention;
Figure 2 is an end view of the engine camshaft shown in Figure 1;
Figure 3 is a partial sectional view on line 3-3 of Figure 1, in the direction of
the arrows;
Figure 4 is an end view of a coupling member that connects the end of the camshaft
to the distributor shaft;
Figure 5 is a sectional view on line 5-5 of Figure 4, in the direction of the arrows;
Figures 6 and 7 are exploded perspective views of the coupling in accordance with
the present invention;
Figure 8 is a side view of the coupling member shown in Figure 4;
Figure 9 is an end view of another coupling member of the coupling in accordance with
the invention;
Figure 10 is a sectional view on line 10-10 of Figure 9, in the direction of the arrows;
Figure 11 is a sectional view on line 11-11 of Figure 10, in the direction of the
arrows; and
Figure 12 is a partial sectional view on line 12-12 of Figure 5, in the direction
of the arrows.
[0008] As is shown in the drawings, with reference more particularly to Figure 1, reference
numeral 10 generally designates an ignition distributor for a four-cylinder internal
combustion engine, the distributor having an annular metallic base portion 12 including
a flange 14. The flange 14 is adapted to be secured to a housing (not shown) of the
internal combustion engine in such a position that the distributor shaft 16 is aligned
with the end of a camshaft 40 of the engine. The distributor shaft 16 rotates within
a sleeve bearing 18 located in a bore formed in the base portion 12.
[0009] The distributor shaft 16 drives a rotor 20 having terminal means 22 that, as the
rotor 20 is rotated, electrically connects a centre electrode 24 sequentially to four
outer electrodes 26 carried by the distributor cap 28. The rotor 20 contains a centrifugal
advance mechanism (not illustrated) which adjusts a metallic bushing 30 relative to
the shaft 16 as a function of engine speed, as is well known in the art. The centrifugal
advance mechanism can for example be of the type disclosed in US-A-3,923,028.
[0010] The bushing 30 carries a rotor 32 formed of magnetic material that has a plurality
of external teeth. The rotor 32 forms part of a magnetic pick-up including an annular
pick-up coil 34 and an annular permanent magnet 36. The pick-up coil 34 and permanent
magnet are rotatably supported as a unit by the upper end of the bearing 18, and this
assembly can be adjusted by a vacuum unit, not illustrated, in order to adjust spark
timing in accordance with manifold vacuum, as is well known in the art. Magnetic pick-ups
of the type described are illustrated for instance in the above-noted US-A-3,923,028.
[0011] The free end of the distributor shaft 16 is connected to the free end of the camshaft
40 of the internal combustion engine by means of a coupling that is generally designated
by reference numeral 42 and will be described in detail hereafter. The coupling comprises
annular parts 44 and 46 constituting a drive member and a driven member respectively.
The annular coupling part 44 is formed of a moulded plastics material such .as a glass-filled
polyamide (nylon), and has a pair of integral tang-like drive lugs 44A which extend
axially from one face 44B of the coupling part 44 and fit within a slot-like groove
40A formed in the end of the camshaft 40. The annular coupling part 46 is formed of
metallic material and has circular holes that receive a tubular pin 48 which extends
through the holes in the coupling part 46 and through a radially extending hole (not
illustrated) formed in the distributor shaft 16, to interconnect the shaft 16 and
the coupling part 46. The pin 48 is press-fitted to the holes in the coupling part
46.
[0012] With reference now more particularly to Figures 2 and 3 of the drawings, it is seen
that the. slot-like groove 40A that is formed in the end of the camshaft 40 extends
substantially radially of the end face 40D of the camshaft and is slightly offset
from the centre axis of the crankshaft, as illustrated. The camshaft 40 has a central
oil passage 40B which intersects the slot-like groove 40A. The inner wall portions
40C of the groove 40A comprise arcuately extending surfaces. The groove 40A can be
formed by the use of a circular side-milling cutter having a diameter of approximately
50 millimetres, whereby the surfaces 40C have the shape of arcs of a circle having
a radius of approximately 25 millimetres. The side walls of the groove 40A are parallel
and extend normal to the arcuately extending walls 40C, as shown in Figure 1.
[0013] The coupling 42 is illustrated in detail in Figures 4 to 12 of the drawings. The
drive lugs 44A of the annular coupling part 44 have inner drive lug surfaces 44C which
are arcuately shaped and are extensions of portions of a circular wall 44D that defines
a central opening 44E formed in the coupling part 44.
[0014] The centre line of the drive lugs 44A is radially offset from a radial centre line
of the annular coupling part 44, as is best illustrated in Figure 4. The amount of
offset corresponds to the amount of offset of the axis of the groove 40A of the camshaft
40 with respect to a radial centre line of the camshaft. The outer surfaces 44F of
the drive lugs 44A are arcuately shaped, as arcs of a circle having a radius of approximately
22.5 millimetres. The distance between one edge 44G of the drive lugs and the face
44B is slightly greater than the distance between the other edge 44J and the face
44B, so that the outer surfaces 44F slant slightly from the edge 44G to the edge 44J,
the difference in these distances being less than 0.5 millimetres.
[0015] The axial length of the drive lugs 44A from the face 44B is so related to the depth
of the groove 40A of the camshaft 40 that the arcuate outer surfaces 44F are spaced
slightly from the arcuate surfaces 40C when the lugs 44A are inserted into the groove
40A and the surface 44B is engaged with the end 40D of the camshaft: as an example,
the surfaces may be spaced apart by a distance of about one-millimetre.
[0016] The width of the camshaft groove 40A is slightly greater than the width of the drive
lugs 44A. For example, the width of the groove 40A may be about 4.50 to 4.53 millimetres
and the width of the drive lugs 44A about 4.39 to 4.47 millimetres.
[0017] The annular coupling part 44 further includes a pair of integral resilient locator
arms 44K. The resilient arms 44K have tooth portions 44L which, as will be described,
snap over the other part of the coupling to hold the coupling parts together and so
prevent their axial separation.
[0018] The annular coupling part 44 further includes a pair of integral drive lugs 44M which
extend in the same direction as the arms 44K. These drive lugs are oblong, and have
curved end portions. The longitudinal axis of the drive lugs 44M is perpendicular
to the longitudinal axis of the drive lugs 44A.
[0019] The annular part 46 constituting the driven member of the coupling 42 is formed of
a metallic material, for example a sintered steel. It has a central circular opening
46A defined by a circular wall 46B, a pair of holes 46C being formed in the wall 46B
for receiving the tubular pin 48. The annular part 46 has a pair of radially extending
grooves 46D which are identical in form and extend from the central opening 46A to
the outer periphery of the part 46. The grooves 46D have a common longitudinal axis
and are rectangular in cross-section, each groove being defined by a bottom wall 46E
and side-walls 46F extending normally to the wall 46E. The walls 46E and 46F of the
two grooves 46D are aligned, and the two grooves 46D together with an intermediate
central semi-circular portion 46G for accommodating the distributor shaft 16 can accordingly
be considered to be a single groove. The annular part 46 further has a pair of oblong
openings 46H extending therethrough, and a pair of through recesses 46J which have
flat inner walls 46K.
[0020] Two elastomeric sleeves, each designated by reference numeral 50, fit over respective
lugs 44M of the annular coupling part 44. The sleeves are formed of a rubber elastomer,
for example an epichlorohydrin-ethylene oxide eopo1ymer: this material is oil-resistant,
and has low-temperature flexibility, flame resistance and elastomeric properties similar
to those of neoprene. The sleeves are shown in their unstretched circular state in
Figures 6 and 7, and in a stretched assembled state in Figure 12. The sleeves have
a rectangular cross-section, as illustrated in Figures 6 and 7. The axial length of
the sleeves 50 is about the same as the axial length of the lugs 44M.
[0021] The method of assembling the coupling of this invention will now be described with
particular reference to Figures 6 and 7. In the assembly of the coupling, the elastomeric
sleeves 50 are slipped over the drive lugs 44M of the annular coupling part 44 so
that after assembly they are stretched to the oblong shape illustrated in Figure 12.
With the elastomeric sleeves embracing the lugs 44M, the coupling parts 44 and 46
are assembled by moving the arms 44K through the oblong openings 46H to a position
in which the tooth portions 44L snap into contact with the flat inner walls 46K of
the through recesses 46J in the coupling part 46. As the arms 44K pass through the
oblong openings 46H they are moved towards each other, and then when the tooth portions
44L move past the walls 46K the arms 44K can spring away from each other to the position
in which the tooth portions 44L engage the walls 46K. As the arms 44K are passing
through the openings 46H, the drive lugs 44M, with the attached elastomeric sleeves,
become positioned within the radially extending grooves 46D, and after the coupling
42 is completely assembled, as shown in Figure 5, the elastomeric sleeves are positioned
within the grooves 46D, as is illustrated in Figure 12.
[0022] The width of the arms 44K is less than the length of the oblong openings 46H, so
that the coupling part 46 can slide relative to the coupling part 46 along an axis
aligned with the axis of the grooves 46D. During this sliding movement the lugs 44M
and the elastomeric sleeves 50 carried thereby slide in the grooves 46D. By way of
example, if the depth of the grooves 46D is 3.35 to3.50 millimetres and their width
is 7.92 to 8.08 millimetres, the axial length of the elastomeric sleeves 50 should
be 3.10 to 3.30 millimetres and the axial length of the drive lugs 44M should be 3.15
to 3.30 millimetres. The width of the drive lugs 44M is 4.30 to 4.38 millimetres,
and each lug 44M is about 7.5 millimetres long. The elastomeric sleeves 50 have a
thickness of 1.89 to 2.39 millimetres. The diameter of a sleeve as measured between
inner walls of a sleeve is about 6 millimetres. The foregoing dimensions are such
that an outer wall of elastomeric sleeve 50 contacts the side walls 46F of the grooves
46D, as shown in Figure 12. The dimensions are further such that the ends of the lugs
44M are slightly spaced from the bottom walls 46E of groove 46D when the flat face
surfaces of the annular parts 44 and 46 are engaged. The engagement of the elastomeric
sleeves with the groove side walls 46F provides some slight frictional force opposing
movement of the lugs and sleeves in the grooves 46D.
[0023] When the coupling 42 is completely assembled as shown in Figure 5, it is secured
to the end of the distributor shaft 16 by aligning the holes 46C in the coupling part
46 with the radially extending hole in the distributor shaft and then press-fitting
the tubular pin 48 into these holes. The end of the distributor shaft 16 extends through
the central opening 46A in the annular coupling part 46 and partially through the
central opening 44E in the coupling part 44 so that the end face of the shaft 16 is
spaced slightly inwardly from the annular face 44B of the coupling part 44. The spacing
is such that when the distributor is assembled to the engine the end face of the distributor
shaft 16 does not contact the end wall 40D of the camshaft 40.
[0024] The coupling device 42 is spring-biased towards the end of the camshaft 40 by a spring
52 that engages a retainer member 54. The retainer member 54 engages a washer 56 which
in turn engages one wall of the annular coupling part 46 of the coupling device. The
retainer member is conventional, and has arms located within recesses formed in the
base portion 12 to prevent rotation of the retainer member. Prior to assembly of the
distributor to the engine, the spring urges the coupling 42 and the distributor.sbaft
l6 to a position in which a portion of the metallic bushing 30 engages an end of the
sleeve bearing 18.
[0025] In assembly of the distributor 10 to the engine, the flange 14 of the base portion
12 is bolted to the engine and the drive lugs 44A engage the end wall 40D of the camshaft
40. With the distributor cap 28 removed, the rotor is rotated by hand, so causing
rotation of the distributor shaft 16 and coupling 42, such that eventually the drive
lugs 44A snap into the slot-like groove 40A formed in the end of the camshaft 40.
After final assembly, the metallic bushing 30 is out of contact with the end of the
sleeve bearing 18. In the final assembled position, the end face 44B of the coupling
part 44 is engaged with the end wall 40D of the camshaft 40. As previously mentioned,
the axial dimension of the drive lugs 44A is such that the arcuate outer surfaces
44F are slightly spaced from the arcuate walls 40C of the slot-like groove 40A formed
in the end of the camshaft 40. The end face of the distributor shaft 16 is slightly
spaced from the end wall 40D of the camshaft 40 so that the ends of the two shafts
do not contact each other.
[0026] The diameter of the distributor shaft 16 is slightly less than the diameter of the
central opening 46A in the coupling part 46, to permit proper assembly of the coupling
42 to the distributor shaft 16. The diameter of the distributor shaft 16 is less than
the diameter of the central opening 44E in the coupling part 44, and the relative
diameter of these parts is selected to permit the coupling part 44 to slide radially
relative to the coupling part 46 by a predetermined amount. This accommodates shaft
misalignment along the longitudinal axis of the grooves 46D. Shaft misalignment along
the longitudinal axis of the drive lugs 44A is accommodated by the fact that the groove
40A in the end of the camshaft will properly receive the drive lugs 44A in various
relative positions of the shafts.
[0027] Voltage pulses generated in the pick-up coil 34 are utilized to control spark timing
in a manner well known in the art. In order to provide proper spark timing, the position
of the distributor rotor 32 should consistently follow the position of the camshaft
40:that is, lost motion between the camshaft and the distributor shaft 16 should be
avoided if consistent spark timing is to be achieved. The coupling of this invention
minimizes lost motion, and it also compensates for torque pulsations of the engine,
which are more severe in four-cylinder engines than in six or eight-cylinder engines.
Lost motion is minimized due to the close fit of the drive lugs 44A with respect to
the camshaft groove 40A, and further the connection between the coupling parts 44
and 46 of the coupling 42 does not permit any substantial relative rotary movement
between these parts. Thus, the elastomeric sleeves 50 completely fill the space between
the lugs 44M and the walls 46F of the grooves 46D, and do not compress to such an
extent as to allow lost motion between the coupling parts 44 and 46. The rectangular
cross-section of the elastomeric sleeves 50 helps prevent lost motion, whereas if
a rubber 0-ring were used instead of the sleeves 50 there would be line contact between
the 0-ring and the mating parts, and the 0-ring could be distorted to permit lost
motion between the coupling parts 44 and 46.
[0028] The elastomeric sleeves 50, as mentioned, reduce noise and also compensate for torque
pulsations of the engine, inasmuch as the elastomeric sleeves in transmitting torque
between the camshaft and the distributor shaft operate to damp
pr smooth out the torque pulsations generated by the engine, and so reduce the adverse
effect of these torque pulsations on ignition timing. Without the elastomeric sleeves
the torque pulsations could, among other things, cause improper operation of the centrifugal
advance mechanism; in general, the application of a sharply varying torque to the
distributor shaft 16 is to be avoided, for proper operation of the distributor.
[0029] As previously mentioned, the drive lugs 44A and the groove 40A in the end of the
camshaft are both offset from the radial centre line of these parts. This is to ensure
that the drive shaft can have only one rotary position relative to the camshaft when
the drive lugs 44A are inserted in the camshaft groove 40A. The openings 46H are both
located to one side of a radial centre line of part 46, so ensuring that the coupling
part 44 will be assembled in the proper relationship to the coupling part 46.
[0030] Because the lugs 44M that carry the elastomeric sleeves 50 are oblong,certain lengths
of each elastomeric sleeve 50 will be in contact with the parallel flat planar side
walls of the lugs and with the parallel flat planar side walls 46F of the grooves
46D, as illustrated in Figure 12. This ensures face-to-face contact between the elastomeric
sleeves and the side walls of the coupling parts over rectangular areas of the elastomeric
sleeves, as opposed to the line contact that would occur if a rubber 0-ring were used.
[0031] The purpose of the through recesses 46J is to accommodate the tooth portions 44L
of the arms 44K so that the tooth portions do not interfere with face-to-face engagement
of the washer 56 and the end face of the coupling part 46. In other words, the ends
of the tooth portions 44L are located within the axial length of the recesses so that
they do not engage the washer 56.
1. A coupling for transmitting drive from a drive shaft (40) to a driven shaft (16),
comprising a first member (44) that is connected to rotate with the drive shaft (40)
and is formed with resiliently-bushed lug means (44M) for co-operation with a respective
radially extending groove (46D) in a second member (46) that is connected to rotate
with the driven shaft (16), characterised in that, for driving the shaft (16) of an
ignition distributor from the camshaft (40) of an internal combustion engine, the
coupling comprises a first member (44) adapted to be driven by the camshaft (40) and
having first lug means (44A) extending axially from one face (44B) thereof in one
direction and further having second lug means (44M) extending axially in an opposite
direction, the first lug means (44A) being adapted to mesh with a groove (40A) formed
in the end of the camshaft (40), the longitudinal axis of the first lug means (44A)
being perpendicular to the longitudinal axis of the second lug means (44M), a driven
second member (46) adapted to be connected to the distributor shaft (16) and having
a radially extending groove (46D) the open end of which faces the first member (44),
the second lug means (44M) being located in the said groove (46D) in the second member,
with an elastomeric sleeve (50) disposed about and engaging the second lug means (44M)
and having outer wall portions engaging side wall portions of the groove (46D) in
the second member(46), and means operative to prevent axial separation of the said
members (44 and 46) while permitting radial movement of the first member (44) relative
to the second member (46) along the longitudinal axis of the radially-extending groove
(46D) in the second member, said last-named means including means (44K, 44L) extending
from one (44) of the members and engaging the other member .(46).
2. A coupling according to claim 1, characterised in that the first lug means (44A)
extending axially from one face (44B) of the first member (44) are adapted to be axially
inserted into the groove (40A) formed in the end of the camshaft (40), and have arcuately
extending outer surfaces (44F) of substantially the same shape as an inner surface
(40G) of the camshaft groove (40A), the radially extending groove in the driven second
member (46) is constituted by radially extending aligned groove portions (46D), and
the second lug means of the first member (44) comprise a pair of axially extending
radially spaced lugs (44M) provided with respective elastomeric sleeves (50) as aforesaid.
3. A coupling according to claim 2, characterised in that the second member (46) has
a pair of slots (46H) extending parallel to the aligned groove portions (46D) therein,
and that the means operative to prevent axial separation of the first and second members
(44 and 46) comprises a pair of arms (44K) extending from the first member (44) through
the slots (46H).and having portions (44L) engaging the second member (46) to prevent
axial separation of the members (44 and 46), the length of the slots (46H) and the
width of the arms (44K) being so dimensioned as to permit limited relative radial
movement of the members (44 and 46) in a direction along the longitudinal axis of
the groove portions (46D) in the second member (46).
4. A coupling according to claim 3, characterised in that the driven second member
(46) has a central opening (46A) for receiving the distributor shaft (16), with the
radially extending aligned groove portions (46D) intersecting the said central opening
(46A) and the pair of radially spaced lugs (44M) of the first member (44) received
in the respective groove portions (46D) at opposite sides of the said central opening
(46A).
5. A coupling according to claim 4, characterised in that the first member (44) is
formed of plastics material, with the first lug means (44A) formed integral therewith
and the second lug means formed as oblong radially spaced lugs (44M) each having parallel
planar side walls, the driven second member (46) is formed of metal, with the radially
extending groove portions (46D) therein of rectangular cross-section, the pair of
arms comprise a pair of flexible arms (44K) formed integral with the first member
(44) and provided with teeth (44L) engaging the second member (46) to prevent axial
separation of the members (44 and 46), and the elastomeric sleeves (50) are of rectangular
cross-section and have planar outer wall portions engaging planar side wall portions
of the grooves (46D) in the second member (46), the axial length of the sleeves (50)
being substantially equal to the axial length of the pair of radially spaced lugs
(44M).